There is a nice, basic guide on using the Revit 2010 Macro Manager in the latest AUGIWorld Magazine.
(LINK UPDATED 14/03/2011)
Check it out if you are interested in the API.
Picture from AUGIWorld Magazine.
Once you get into Revit programming, check out The Building Coder.
There is also an article in the magazine on Autodesk Impression, if you are interested.
